Method for cracking aliphatic hydrocarbons



United States Patent 3 60 t METHOD FOR. CRACKING ALlPH-ATIC HYDROCARBONS M William N. Vand'erkooi and Ri'chardA'. -Mock, Midland, Mich., assignors to The Dow Chemical Company, Midland, Micht, a corporationof Delaware I Filed-Nov. 19, 1962, Star, No.-238,'502' '6- Claims. (Cl. 260---673) The presentinvention relates to a. novel method. for cracking aliphatic hydrocarbons and hydrocarbon mix-' tures predominantly olefinic in character to produce aromatic hydrocarbons of the benzene series, ethylene and butadiene as ,the primary products. More particularly the present invention concerns a novel. process employing certain metals as promoters whereby improv ed yields of useful products are obtained from refinery by-products predominantly olefinic in characternot readily assimilated by the petrochemical phases of. the industry. As is often the case in operating. arefinery, there are periods wherein the production of by-products becomes so large as to present a storage problem" Other times when certain acyclic and cyclic unsaturates would be useful if available they are produced in shortsupply. It would thus be advantageous to have a process whereby various by-products or oversupply of aliphatic hydrocarbons particularly ones olefinic in character, as well as mixtures of olefins and methane or ethane could -readily be converted to one of several cyclic orQacyclic materials readily assimilated by the petrochemicals industry.

There is voluminous art on cracking and reforming naphthas and the like. The majority ofit' concerns it'self with wet cracking (cracking in the presenceof steam) and that which does concern itselfwith dry cracking (cracking in the absence of steam) empl'oys'cat'alysts, techniques and/or materials of construction, in furnace and associated reaction equipment, which are taught to be critical to successful operation.

One piece of art which concerns dry crackingis US. Patent No. 2,735,876, which teaches. that surface-tovolume ratios of the reactor are critical The same reference also teaches the pyrolytic reaction must. be carried out in the absence of nickeLJthat is, the reactor and associated equipment must be of nickel free" steel. Further, the reference teaches soaking" at about reactor temperature for up to 40 seconds. This latter charge is undoubtedly attributable to investigations such-as carried out by Hurd et al;, J.A.C.S. 51 4978-4990 (19-30), who ran hydrocarbon gases throughmonel steel reactors at 250 C. and found destructive cracking to carbon and tarry material to be the major identifiable products.

It was thus surprising to find that an aliphatic hydrocarbon feed predominantly olefinic innature could be advantageously pyrolytically cracked and reformed in the absence of steam and that this pyrolysis reaction'was actually promoted by carryingout the reaction in the presence of ferrous alloys containing nickel, cobalt or molybdenum. During our investigations it was found also that, contrary to theteachings in the literature, the desirable cracked and reformed reaction products would not increase during a soaking period, that is, holding reaction mass at about reaction temperature for a period, after pyrolytic reaction in the absence of steam and in Patente'd Apr; 5,. 1966- ace.

the presenc'e ofone of the aforementioned metal alloys. Rather,- when soaking was employed, under the conditions of the present invention? the soaker" and even the reactor furnace would cokempf i.c., become fouled with tarry and-carboniferous products ofanunde'sirable character. Thus, no soaking is employed in the present process. It was found that the product distribution did not vary appreciably with broad changes in the temperature and residence time. Further, the use of mixtures of the aforementioned hydrocarbon feeds with" methane and ethane whether or" not carried out in the presence of the alloy resulted in product distribution not heretofore achieved.

The figure illustrates. the computer calculated curve representing the average weight" percent yield of each product group in the converted product stream at the indicated percent conversion per pass of propylene by pyrolytic cracking in the absence of steam in a steel alloy reactor.

The present invention, the pyrolytic cracking and reforming of thei'aforementioned hydrocarbon feeds, individually or mixtures thereof, to ethylene, butadiene, benzene and" alk'ylbenzenes a's'the principalandprim'ary products, is achieved byintroducing' the-feed stock into a directly or indirectly furnace-fired reactor in amanner such that the reactantsi are in contact with-steel" alloys containing nickel, cobalt and/or molybdenum,,metals. in substantial proportions: as the principal. alloying. metal, the furnace being heated to temperatures. of? from about 500 to about 1200 C. but preferably from about 650 to 900 C., maintaining the feed stock in the furnace for from 0.01 to about 50 seconds, and preferably from about 0.1 to 20 seconds; and, immediately quenching the exit gases to'bel'ow the atmospheric boilingtemperature of the aromatic; products; The cooling on quenching step promotes the physical separation of the aromatic constituents ofthe product. mixture fromv the aliphatic constituents. Further separation of the" various products of the reaction. can be accomplished in. coventional manner known to the art, such as fractional distillation, and the like The temperature range above: is most advantageous when the furnacev surface-torvolume ratio is between about 50:1-ft.- -to 5:1 ft.

Pressure is' not a critical: factor in. the conversion or the product distribution. No adverse effects have been observed when the furnace is. operated at from about atmospheric pressure to about 100 p.s.i.g.

The following examples illustrate the present invention but are not to be construed as limiting:

Example 1 To illustrate the significant advance which the present invention makes over the known art, the following comparative runs were made: 0

Two reactors were prepared having identical internalexterna-l dimensions. One reactor was prepared from Incoloy' nickel steel (analysis: 30-35% Ni, 19-23% Cr, Fe remainder with trace amountsof C, Mn, S, Si, and 0n) the other from 446 stainless steel (a nickel-free chrome steel). Both reactors were run at various temperatures and the residence time adjusted to obtainian conversion of reactants. The product stream was'passedtlirough a glycol-cooled heat exchanger and immediately analyzed. The following table sets forth the residence time required in the reactor to produce an 80% conversion of the pure propylene feedstockr .Ihe product distribution from both runs was substantially identical. The propylene was fed to the reactors, each having a 1 inch ID. and length of 31 inches, at rates corresponding to the residence times in the following table.

Residence time in seconds Temperature,

C. Incoloy 446 stainless steel Y By weight Temperature, Residence percent con- Reactcr 0. time (see) version,

propylene 1 1 Product distribution was as indicated in the figure.

Example 2 To deter-mine the effect of steam as a diluent in the nickel alloy promoted reaction the following experiment was made: 1 p

A 1 inch I.-D. Incoloy pipe-31 inches long containing a thermocouple well was surrounded with an electric heater along its length. The reactor was held at 800 C. :5" C. throughout each run. Feed stock was preheated to 500 C., and the dry cracking runs were made using a flow rate of 270 grams per hour of propylene. Wet cracking runs were made using 170 grams of propylene and 80 grams of steam per huor. The residence time for each run was the same, and the product analysis for each run is set forth in the following table.

4 Thus, it is clearly demonstrated that dry cracking in the presence of an alloy of steel containing nickel produces more aromatic products, less oxides of carbon, and more ethylene than corresponding Wet cracking procedures.

Example 3 Crude propylene, containing 3.5% propane, 1.5% propadiene, 1.5 methyl acetylene, 0.1% butenes, 200 ppm. H 8, 100 ppm. RSH, and 150 ppm. COS, was passed through a reactor consisting of 127 ft. of 2-inch ID. 310 stainless steel pipe'(l8% Ni; 8% Cr) in a gas fired furnace. The propylene, fed at 380 lb./hr., entered the reactor at ambient temperature and 3 p.s.i.g., was raised to 700 C. in the first 35 feet of pipe and left the reactor at 835 C. After leaving the reactor the hot gases were rapidly cooled to 50 C. by a recirculating oil quench system. The exit gas pressure was atmospheric. After 12 days of operation the input pressure increase was less than /2 p.s.i., which indicates negligible coke nad tar build-up in the reactor. Complete analyses of the outlet stream indicated 79% of the propylene had reacted. The product yield pattern in weight percent based on the reacted'propylene was as follows:

Hydrogen 0.9 Methane 18.8 Ethane 1.7 Propane 0.6 Butanes 0.6 Ethylene 30.5 1,3-butadiene 2.7 Butenes 1.3 Pentenes 1.0 Pentadienes 7.1 Hexenes 0.2 Benzene I 14. Toluene 3.4 Ethylbenzene 0.1 Xylenes 0.4 Styrene 2.6 Methylstyrenes 0.6 Indane 0.2 Indene 1.3 Napthalene 2.9 Methylanthracene 0.8 Methylnaphthalene 0.4 Diphenyl 0.6 Acenaphthalene 0.2 Others 6.9

This example demonstrates that propylene can be successfully and beneficially cracked at high conversion for ad vantageously prolonged operating periods in a nickel steel reactor without the use of steam or soaking drum and with very little coke formation.

Example 4 To illustrate the enhanced reactivity of propylene in a nickel-containing reactor, the furnace as described in 7 Example 3 was duplicated to provide one bank from 446 nickel-free stainless steel and another bank from 310 Ni-Cr-stainless steel and both banks placed in the same gas fired furnace. Crude propylene was fed at a rate of 380 pounds per hour to each bank. The exit temperature of each bank was 808 C. The conversion of propylene in the 446 SS. tube bank was 46% while the conversion in the 3lO-Ni-Cr S.S. tube bank was Five months of operation resulted in the 446 tube bank sagging out of shape while the 310 bank remained substantially unaffected, illustrating the superior structural characteristics of the nickel-containing reactor under the desired pyrolysis conditions.

Example 5 Using the Incoloy reactor described in Example 2, mixed butenes were dry cracked at 800 C. The feed contained 0.02 propane, 2.0 propene, 9.6 butane, 26.7 l-butene, 45.0 isobutene, 11.2 trans-Z-butene, 5.2 cis-2- butene and 0.2 1,3-butadiene. The butenes were fed into the reactor at the rate of 500 grams per hour, and reactant conversion was 87%. Analysis of the hot gas leaving the furnace showed it to contain in weight percent the following:

Hydrogen 0.7 Methane 20.1

Ethane 2.1 Propane 0.3 Butanes 1.2 Ethylene 16.8 Propylene 12.4 1,3-butadiene 2.9 Butenes 12.8 Pentenes 0.4 Pentadienes 0.8 Hexenes 0.5 Benzene 10.0 Toluene 5.6 Ethylbenzene 0.4 Xylenes 1.0 Styrene 2.0 Methyl styrenes 0.8 Mesitylene 0.1 Indane 0.2 Indene 1.0 Naphthalene 3.0 Methylanthracene 0.4 Met-hylnaphthalene 0.6 Diphenyl 0.4 Acenaphthalene 0.2 Others 3.3

After hours of operation in the laboratory unit, only 5 minutes were required to burn out carbon with air at such a rate as to maintain gas stream temperature in the reactor at 100 C. This indicates that the rate of coke formation from dry butene cracking is very low.

Example 6 To illustrate the advantage of adding a lower alkane to the olefin feed three experiments were run in a 446 stainless steel 1 inch I.D., reactor 31 inches long. The total flow rate through the reactor in each experiment was 200 L/hr. (measured at 25 C. and 1 atmosphere pressure) and the reactor was maintained at 830 C. In one experiment the feed was pure propylene, in another the feed was a 1:1 by volume mixture of methane and propylene, and in the third the feed consisted of a 1:1 by volume mixture of argon and propylene. The temperature of the reactor and residence time of the feed were held constant in all three experiments while varying the composition of the gas feed. The weight percent product yield distribution based on reacted propylene are given in the following table. In the experiment with methane the amount of methane in the feed was subtracted from that in the outlet stream before calculating the product yields obtained from the propylene.

1:1 1: 1 Hydrocarbon teed Propylene methaue- Argonpropylene propylene Propylene conversion, percent- 82 60 Product distribution, weight percent: Hydrogen 1. 4 2. 0 2. 7 Methane 23. O 20. 0 35. 0 2. 7 2. 0 2. 2 36. 9 46. 8 38. 1 2. 1 2. 3 7. 7 1. 2 1. 5 5. 7 1. 1 1. 6 0. 5 0. 2 1. 0 0. 0 11. 9 11. 3 4. 6 3. 9 3. 0 0. 8 5. 7 4. 7 1. 0 4. 0 3. 7 0.9 Polycyelies 5. 9 0. 1 0. 8

The experiments with argon show that dilution with an inert material increases the methane yield from propylene while decreasing the yield of liquid products. The addition of methane, however, to the propylene feed significantly increases the yield of ethylene from propylene while having no adverse effect on the yields of the desirable liquid aromatic species. Thus, the addition of readily available and cheap methane can be used to advantageously improve the ethylene yield obtained from dry cracking propylene.

We claim:

1. A method for cracking aliphatic hydrocarbons which comprises pyrolyzing by passing aliphatic hydrocarbon feed predominantly olefinic in character through a heated zone at such a rate as to have a residence time of from about 0.01 to about 50 seconds, at a temperature substantially inversely related of from about 500 C. to about 1200 C., substantially in the absence of water vapor and at about atmospheric pressure, in contact with surfaces of an alloy of a major proportion by weight of iron and a minor proportion of nickel, alloyed with said iron and immediately cooling the effiuent gas from said reactor to below the atmospheric boiling point of the aromatic constituents of the efliuent stream and collecting the same and simultaneously collecting the aliphatic constituents which pass through the cooling step as gases.

2. The method of claim 1 wherein the surface-tovolume ratio of reactor is 50:1 to 5:1 ft.

3. The method of claim 1 wherein the aliphatic feed is essentially an olefinic hydrocarbon.

4. The method of claim 3 wherein the residence time is from 0.1 to 20 seconds.

5. The method of claim 1 wherein the hydrocarbon is a mixture of from -80% by weight of an olefin and from 0 to 20% by weight of a saturated aliphatic (alkane) having from 3 to 10 carbon atoms.

6. The method of claim 1 wherein the pressure in the reaction zone is from about 1 to about 100 p.s.i.g.

References Cited by the Examiner UNITED STATES PATENTS 1,945,960 2/ 1934 Winkler et al 260673 1,986,239 1/ 1935 Winkler et al. 260673 1,987,092 1/ 1935 Winkler et a1. 260673 2,033,878 3/1936 Burk 260673 2,038,834 4/ 1936 Frey 260673 2,123,799 7/1938 Podbielniak 260673 2,168,840 8/ 1939 Groll 260673 ALPHONSO D. SULLIVAN, Primary Examiner. 

1. A METHOD FOR CRACKING ALIPHATIC HYDROCARBONS WHICH COMPRISES PYROLYZING BY PASSING ALIPHATIC HYDROCARBON FEED PREDOMINANTLY OLEFINIC IN CHARACTER THROUGH A HEATED ZONE AT SUCH A RATE AS TO HAVE A RESIDENCE TIME OF FROM ABOUT 0.01 TO ABOUT 50 SECONDS, AT A TEMPERATURE SUBSTANTIALLY INVERSELY RELATED OF FROM ABOUT 500*C. TO ABOUT 1200*C., SUBSTANTIALLY IN THE ABSENCE OF WATER VAPOR AND AT ABOUT ATMOSPHERIC PRESSURE, IN CONTACT WITH SURFACES OF AN ALLOY OF A MAJOR PROPORTION BY WEIGHT OF IRON AND A MINOR PROPORTION OF NICKEL, ALLOYED WITH SAID IRON AND IMMEDIATELY COOLING THE EFFLUENT GAS FROM SAID RE- 